The overall goal of the proposed research is to understand the physiological role of protein arginine methylation and its impact on the maturation of mRNA in the yeast Saccharomyces cerevisiae. Given the prevalence of this post-translational modification among RNA metabolism enzymes, it is likely to play an important role in the process. In exploring this hypothesis further, the first aim will be to analyze the impact of arginine methylation on Hrp 1p, an essential yeast protein that is a member of a class of proteins termed heterogeneous nuclear ribonucleoproteins or hnRNPs. To provide a foundation for this analysis, the dimethylarginine residues within Hrp 1p will first be mapped. Next, the effect of this modification on three Hrp 1p activities will be assayed; l) mRNA 3'-end processing, 2) RNA-binding, and 3) nucleocytoplasmic shuttling. The second aim examines whether protein arginine methylation represents a signaling mechanism by determining the reversibility of the process. If so, the plan is to identify and characterize the corresponding demethylase. The third aim utilizes a combination of biochemical and molecular biological approaches to identify and characterize proteins that physically interact or functionally overlap with the protein arginine methyltransferase enzyme (Hmt1p). As part of this aim, cellular proteins that receive this modification will be cataloged. The objective is to learn where these proteins are localized in the cell, and whether they share common sequences and cellular activities. Since the structures of arginine methyltransferases have been well conserved from yeast to human cells, the genetically amenable yeast Saccharomyces cerevisiae represents an ideal model organism for these studies. Recent data implicates some human arginine methylated proteins in molecular diseases (i.e. FMR1: Fragile X Mental Retardation Syndrome). Additionally, the presence of methylated arginines among viral RNA maturation enzymes implies a role for this modification in viral mRNA processing (i.e. herpes simplex ICP27). Furthermore, human arginine methylated hnRNPs participate RNA metabolism which impacts additional cellular processes. A better understanding of arginine methylation should not only enhance the understanding of cellular RNA maturation, but also provide insights into viral mechanisms for RNA maturation during cell infection.